冷却速率对GWZ1032K合金中14H-LPSO结构形成的影响

EFFECT OF COOLING RATE ON THE FORMATION OF 14H-LPSO STRUCTURE IN GWZ1032K ALLOY

采用金属型铸造和慢速凝固,在不同冷却速率下制备了Mg-10Gd-3Y-1.8Zn-0.5Zr(质量分数,%)(GWZ1032K)合金.采用SEM,TEM和XRD研究了冷却速率不同的GWZ1032K合金的组织和相构成.在GWZ1032K合金中,α-Mg基体中的层片状14H-LPSO结构随着冷却速率的下降而增加,在冷却速率为0.005℃/s的试样中充满了整个晶粒;随着合金冷却速率降低,GWZ1032K合金中晶界第二相分别由5℃/s时的(Mg,Zn)_3RE相转变为0.5和0.1℃/s时的(Mg,Zn)_3RE相和14H-LPSO结构的χ相共存;在0.01和0.005℃/s时只有14H-LPSO结构的χ相.结果显示在接近于平衡凝固的缓慢冷速条件下,更容易形成具有稳定结构的层片状14H-LPSO结构和χ相.在冷却速率为0.5和0.1℃/s时,(Mg,Zn)_3RE共晶相和χ相共存,(Mg,Zn)_3RE共晶相和χ相的位向关系为[110]_(χphase)∥[(?)23]_((Mg,Zn)_3RE)和∠g(001)_(χphase)g(110)_((Mg,Zn)_3RE)=8.4°.

Mg-10Gd-3Y-1.8Zn-0.5Zr（mass fraction,%）（GWZ1032K） alloys were fabricated by permanent mold casting and slow solidification with different cooling rates.The microstructures of the GWZ1032K alloys with different cooling rates were investigated by SEM,TEM and XRD.Two kinds of LPSO structure were observed,include lamellar 14H-LPSO structure in the grain interior andχphase at the grain boundaries.Lamellar 14H-LPSO structure inα-Mg matrix propagated in the matrix with the decease of solidification rate,and filled the whole grain in the alloy solidified at 0.005℃/s.The second phase in the alloys also changed with deceasing the solidification rates,there are （Mg,Zn）3RE compounds only when solidification rate is 5℃/s,（Mg,Zn）3RE compounds and 14H-LPSO structuredχphase when solidification rates are 0.5 and 0.1℃/s,and 14H-LPSO structuredχphase only when solidification rates are 0.01 and 0.005℃/s.It was detected that（Mg,Zn）3RE compounds andχphase existed simultaneously at the grain boundaries in the alloys at solidification rates of 0.5℃/s and 0.1℃/s,and the orientation relationship between them was determined to be [110]（χphase）//[（223]（（Mg,Zn）3）RE and∠（001）（χphase）（110）（（MgZn）3RE）=8.4°.